The Metabolomics Core provides comprehensive analytical support for investigators in the diabetes and obesity mouse research community. The focus of the Metabolomics Core will be on providing panels of relevant metabolic measurements, rather than single-point measurements, to clearly assess the consequences of changes in gene expression. An equally important aspect of the Metabolomics Core is the measurement of isotopic enrichment in an array of metabolites. The use of stable isotopes has become an essential component of modern methods to characterize metabolic flux. An important new initiative of the Metabolomics Core is the analysis of concentrations and fluxes of gut microbial-derived metabolites. The services provided by the Metabolomics Core include the extraction, purification, derivatization, and instrumental analysis of metabolites and selected enzyme activities from tissues and plasma. The methods have been scaled to account for the minimal amounts of tissues (~10 to 25 mg, and plasma volumes of ~ 5 to 25 l) that can be provided by investigators. The facility is equipped with an array of state-of-the-art instrumentation, including GC-MS, LC-MS/MS, and NMR, providing the flexibility and resources for analyses of metabolite concentrations as well as isotopic enrichments. Metabolic panels of serum, plasma, and urine, including Chem 7, liver function tests, lipid profiles, and divalent cations, are obtained using the COBAS MIRA system optimized for analysis of the mouse samples such that required volumes average ~20 l of serum for any combination of 4 tests. These plasma chemistry assays fill a need with very high demand for mouse studies, as reflected in our work flow over the last funding period. GC-MS and LC-MS/MS analyses provide complete profiles of chain length distribution of fatty acid metabolites, included free fatty acids, fatty acyl-CoA esters, diacylglycerols, ceramides. Other LC-MS/MS that are offered and are in high-demand include intermediates of glucose metabolism for metabolic flux measurements, and creatinines for renal clearance. The Metabolomics Core is a resource lab for the analysis of samples generated during the course of experiments of the Integrative Physiology Core and the Microbiome and Animal Care Core at the Yale MMPC, and also provides the same array of assays to other outside investigators to assist in phenotyping of transgenic mouse models of diabetes. Samples are analyzed on a fee-for-service basis with the charge per assay based on policy determined by the National MMPC Executive Committee, designed to provide substantial savings to NIH-funded users compared to commercial vendors. The Core has an active Research and Development Program to develop new analytical protocols to address new and exciting developments in the biochemistry of diabetes, obesity, and associated complications.